The availability of voice over packet network technology and in particular, although not exclusively, corporate multimedia network, circuit switched and packet switched network technology has provided users with new services and functionalities which had not been available in the conventional telephony technologies. For example, the Internet or other private packet switched networks (multimedia data networks) or Internet-based multimedia communication technologies do not only offer advanced speech processing but also audio, video and/or other more advanced data communication services.
Due to the intrinsic packet switched nature, products for allowing the integration of these new Internet-based multimedia communication technologies with the older but more widespread and well-known traditional circuit switched telephony technologies are necessary. Since there is an exponential growth of the Internet and therefore of the multimedia data networks that support it, the number of potential customers for Internet-based multimedia communication systems increases every day. However, of course these customers still want to have access to the traditional circuit switched telephony systems, e.g. to a private branch exchange system PABX or generally to a circuit switched private communication network (PCN).
Each “world”, namely the circuit switched technology and the packet switched technology, must be interfaced as regards the usage of their protocols for signaling and communication in order to allow a communication between these two apparently so different “worlds”.
The two “worlds” are indeed completely different regarding the call set up and the call routing and other functionalities. Whilst in a circuit switched network PABX the first subscriber stations TT set up calls between each other by simply dialing the directory number whilst the switching means SW will connect the call, multimedia terminals MT being based on a packet switched technology operate completely differently. In a multimedia data network the multimedia terminals have transport addresses, identifications like an e-mail address, a URL, user name etc., an authentication (password) and have specific capabilities like audio, video, data, or multiconference functionalities. Conventionally, in a multimedia data network the multimedia terminals MT can have a “freeseating feature”, e.g. they can be connected to the multimedia data network at arbitrary connectors. In the multimedia data network the multimedia terminals MT perform a registration procedure which makes them known within the multimedia data network. All such features are intrinsically different to the circuit-switched technology in traditional private branch exchange systems PABX.